ALL reasonably sophisticated operating systems are the same in that they all provide "standard" features that more or less define the purpose of an OS:

• Hardware-level I/O
• Job control
• Memory management
• Task switching
• Utilities for management

• Similar file structure (subdirectory tree) and concepts:
• /users/dierdorf/graphics/Becky Portrait.small.jpg is a legal file name
• . (current dir), .. (parent) have same meaning.
• | (pipe), filters, stdin/stdout, > (redirection), path, current directory, * (wildcard), etc.
• Because of similar structure, Linux can read and write DOS/Windows (FAT, FAT32, etc.) partitions in addition to its "native" ext2.
• Command Interpreter, aka the shell - like  DOS's command.com.
• Environment variables.
• Similar command line utilities:
• ls        =  dir
• rm      =  del
• mv     =  move (and rename)
• cp      =  copy
• fsck   =  chkdsk
• cd      =  cd
• Batch files.
• Files are executable (binary or batch) or data.
• User has choice of command line shell, GUI, or both.